Heart Failure (HF) is a common event in childhood with significant morbidity and mortality. Current research indicates that cardiomyocyte apoptosis may contribute significantly to the development of HF. We have recently demonstrated that ROCK1 (Rho-associated, coiled-coil containing protein kinase 1) is a key mediator which links pro-apoptotic stimuli to apoptosis in neonatal cardiomyocytes. Our results suggest a model wherein low levels of activated caspase 3 directly cleave and activate ROCK1;activated ROCK1 in turn amplifies caspase 3 activation, resulting in a marked amplification of cardiac apoptosis. Importantly, this mechanistic relationship between ROCK1 activation and caspase 3 activation occurs in failing human hearts, suggesting that this pathway is a valid therapeutic target. The experiments proposed in Project 2 will further validate the importance of, as well as establish the mechanistic underpinnings of, ROCK1-mediated cardiomyocyte apoptosis. Specific Aim 1 will characterize the role of ROCK1 activation in cardiomyocyte apoptosis. Initial experiments will establish the importance of caspase 3-dependent ROCK1 activation on cardiomyocyte survival and HF progression following treatment with cardiotoxic drugs which induce childhood HF. Other studies will test the hypothesis that ROCK1 activation is sufficient to amplify caspase 3 activation and induce cardiomyocyte apoptosis in vivo. Experiments proposed in Specific Aim 2 will establish the molecular mechanism by which activated ROCK1 induces cardiomyocyte apoptosis. Initial studies will test the hypothesis that activated ROCK1 amplifies caspase 3 activation via post-mitochondrial regulation. Other studies will determine if TAT-based delivery of anti-apoptotic proteins can attenuate activated ROCK1-induced cardiomyocyteapoptosis in vitro, and if warranted, in vivo. Collectively, the experiments proposed in Project 2 will test the hypothesis that ROCK1-mediated amplification of caspase 3 activation plays a critical role in cardiomyocyte apoptosis, and furthermore will establish the role of ROCK1 signaling in response to acquired myocardial injuries which lead to childhood HF. This project will also determine if manipulation of ROCK1 signaling can be exploited to therapeutically inhibit cardiomyocyte apoptosis in a mouse model of acquired postnatal HF.